Method for making a ceramic mold

Abstract

A new method for producing a composite ceramic mold for production of metal castings is disclosed. The composite mold is comprised of a backing layer and a facing layer. The backing layer is formed by pouring a mixture of a suitable refractory, a gelling agent, and a binder about an oversized pattern. After the backing layer hardens, it is fired and then baked. The facing layer is then formed integrally with the backing layer by pouring a mixture of comminuted highly refractory material, a gelling agent, and a binder between the oversized backing layer and a dimensionally-correct pattern. After the facing layer hardens, it is fired and then baked.

I claim: 
     
       1. A method for making a composite ceramic mold, comprising: a) forming a backing layer composition comprised of a refractory material, a binder, and a gelling agent;   b) permitting said backing layer composition to gel to form a backing layer comprising a cavity having a cavity surface;   c) firing said backing layer;   d) baking said backing layer;   e) scoring said cavity surface;   f) forming a facing layer composition comprised of a highly refractory material, a binder, and a gelling agent;   g) permitting said facing layer composition to gel to form a facing layer integral with said fired and baked backing layer;   h) firing said integral facing and backing layers; and   i) baking said integral facing and backing layers.   
     
     
       2. The method of claim 1 wherein said refractory material used to form said backing layer composition comprises a material selected from the group consisting of sodium silicate, sand, calcinated mullite, and mixtures thereof. 
     
     
       3. The method of claim 1 wherein said highly refractory material used to form said facing layer composition comprises a material selected from the group consisting of zircon, zircon flour, fused silica, aluminum silicate, and mixtures thereof. 
     
     
       4. The method of claim 2 wherein said highly refractory material used to form said facing layer composition comprises a material selected from the group consisting of zircon, zircon flour, fused silica, aluminum silicate, and mixtures thereof. 
     
     
       5. The method of claim 1 wherein said binder comprises a silicate selected from the group consisting of lower alkyl silicates, ethyl silicates, organic silicates, and combinations thereof. 
     
     
       6. The method of claim 1 wherein said binder yields an alcohol on hydrolysis. 
     
     
       7. The method of claim 2 wherein said binder comprises a silicate selected from the group consisting of lower alkyl silicates, ethyl silicates, organic silicates, and combinations thereof. 
     
     
       8. The method of claim 3 wherein said binder comprises a silicate selected from the group consisting of lower alkyl silicates, ethyl silicates, organic silicates, and combinations thereof. 
     
     
       9. The method of claim 4 wherein said binder comprises a silicate selected from the group consisting of lower alkyl silicates, ethyl silicates, organic silicates, and combinations thereof. 
     
     
       10. The method of claim 1 wherein said gelling agent comprises an aqueous acid. 
     
     
       11. The method of claim 2 wherein said gelling agent comprises an aqueous acid. 
     
     
       12. The method of claim 3 wherein said gelling agent comprises an aqueous acid. 
     
     
       13. The method of claim 4 wherein said gelling agent comprises an aqueous acid. 
     
     
       14. The method of claim 5 wherein said gelling agent comprises an aqueous acid. 
     
     
       15. The method of claim 7 wherein said gelling agent comprises an aqueous acid. 
     
     
       16. The method of claim 8 wherein said gelling agent comprises an aqueous acid. 
     
     
       17. The method of claim 9 wherein said gelling agent comprises an aqueous acid. 
     
     
       18. The method of claim 5 wherein said ethyl silicate comprises approximately 18.5-21.0% by weight silicon. 
     
     
       19. The method of claim 7 wherein said ethyl silicate comprises approximately 18.5-21.0% by weight silicon. 
     
     
       20. The method of claim 8 wherein said ethyl silicate comprises approximately 18.5-21.0% by weight silicon. 
     
     
       21. The method of claim 9 wherein said ethyl silicate comprises approximately 18.5-21.0% by weight silicon. 
     
     
       22. The method of claim 3 wherein greater than about 50% by weight of the highly refractory material has a particle size of 100 mesh or finer. 
     
     
       23. The method of claim 4 wherein greater than about 50% by weight of the highly refractory material has a particle size of 100 mesh or finer. 
     
     
       24. The method of claim 9 wherein greater than about 50% by weight of the highly refractory material has a particle size of 100 mesh or finer. 
     
     
       25. The method of claim 22 wherein the particle sizes of said highly refractory material ranges from about 30-325 mesh. 
     
     
       26. The method of claim 23 wherein the particle sizes of said highly refractory material ranges from about 30-325 mesh. 
     
     
       27. The method of claim 24 wherein the particle sizes of said highly refractory material ranges from about 30-325 mesh. 
     
     
       28. The method of claim 2 wherein greater than about 50% by weight of the refractory material has a particle size of 200 mesh or coarser. 
     
     
       29. The method of claim 1 wherein said backing layer and said facing layer are fired at a temperature of about 400° to 500° F. 
     
     
       30. The method of claim 29 wherein said backing layer is fired for a period of about 2 hours and said integral facing and backing layers are fired for a period of about 30 minutes. 
     
     
       31. The method of claim 1 wherein said backing and said facing layers are baked at a temperature of about 1700° F. 
     
     
       32. The method of claim 31 wherein said backing layer is baked for a period of about 16 hours and said integral facing and backing layers are baked for a period of about 4 hours. 
     
     
       33. A method for making a composite ceramic mold, comprising: a) combining a refractory material with a binder and a gelling agent, and forming a backing layer therefrom, said backing layer comprising a cavity having a cavity surface;   b) firing said backing layer;   c) baking said backing layer;   d) scoring said cavity surface;   e) combining a comminuted, highly refractory material suitable for metal casting with a binder and a gelling agent, and forming a facing layer therefrom integral with said fired and baked backing layer;   f) firing said integral facing and backing layers; and   g) baking said integral facing and backing layers.   
     
     
       34. A method for producing refractory molds which comprises: a) preparing a first slurry comprising a refractory material, a binder, and a gelling accelerator;   b) pouring said first slurry over an oversized pattern, allowing the first slurry to gel, immediately separating the gelled mass of the first slurry from the oversized pattern, immediately thereafter firing the gelled mass of the first slurry and allowing it to burn until the flammables or evaporables are consumed, baking said fired gelled mass of the first slurry and scoring the surface of the resulting baked mass originally contacting said oversized pattern;   c) preparing a second slurry comprising a comminuted, highly refractory material, a binder, and a gelling accelerator;   d) pouring said second slurry between said scored surface of said fired and baked mass of the first slurry and an actual-dimension pattern, allowing the second slurry to gel and affix integral to said fired an baked mass of the first slurry, immediately separating the integral gelled mass of the second slurry and the fired and baked mass of the first slurry from the actual-dimension pattern, immediately thereafter firing the gelled mass of the second slurry and allowing it to burn until the flammables or evaporables are consumed, then baking said fired gelled mass of the second slurry.   
     
     
       35. The method of claim 34 wherein said oversized pattern comprises said actual-dimension pattern further comprising a spacing layer. 
     
     
       36. The method of claim 35 wherein said spacing layer comprises clay. 
     
     
       37. The method of claim 35 wherein said spacing layer comprises wax. 
     
     
       38. The method of claim 34 wherein said binder comprises a liquid lower alkyl silicate. 
     
     
       39. The method of producing an inexpensive, sturdy, highly refractory mold for metal casting including a backing body and a facing which comprises: a) manufacturing said backing body from a mixture of refractory material, a binder, and a gelling agent, and pouring said mixture over an oversized pattern, permitting it to gel, immediately separating said gelled backing body from said oversized pattern, immediately thereafter igniting said backing body to burn any volatiles or evaporables in said backing body until said volatiles are consumed or said evaporables are released, baking said backing body and scoring the surface of the backing body originally contacting said over-sized pattern;   b) placing said backing body over an actual-dimension pattern thereby defining a space between said backing body and said actual-dimension pattern;   c) manufacturing said facing from a mixture of highly refractory material, a binder, and a gelling accelerator and filling said space between said backing body and said actual-dimension pattern with said mixture, permitting said mixture to gel and attach integral to said scored surface of said backing body, separating said actual-dimension pattern from said integral gelled facing and backing body, igniting said gelled facing to burn any volatiles or evaporables in said facing until said volatiles are consumed or said evaporables are released, and then baking said facing.   
     
     
       40. A method for making a composite ceramic mold comprised of a backing layer formed from a refractory material suitable for metal casting, a binder, and a gelling agent, and an integral facing layer formed from a comminuted, highly refractory material suitable for metal casting, a binder, and a gelling agent, wherein both the backing layer and the facing layer are fired and then baked, wherein the improvement comprises: firing and baking said backing layer and scoring the baked backing layer on its surface that contacts the facing layer prior to forming integral therewith said facing layer, and then firing and baking said integral facing and backing layers.